The present invention generally relates to the use of self degrading materials in subterranean operations, and, more specifically, to the use of self degrading materials prior to re-fracture treatments in subterranean operations.
Many petroleum-containing formations require some form of stimulation treatment to economically produce hydrocarbons. Stimulation treatments can be performed upon completion of the well construction or later in the life of the well after producing hydrocarbons. As production drains the reservoir, secondary stimulation treatments can also be used to enhance the production rate of a well.
Oil or gas residing in the subterranean formation may be recovered by stimulation treatments, which fall into two main groups: hydraulic fracturing and matrix treatments. Fracturing treatments are performed above the fracture pressure of the subterranean formation to create or extend a highly permeable flow path between the formation and the wellbore. Matrix treatments are performed below the fracture pressure of the formation. Other types of completion or intervention treatments can include, for example, gravel packing, consolidation, and controlling excessive water production.
The completion of a horizontal well is often designed to have mechanical barriers along the wellbore for isolation of multistage fracture treatments. These mechanical barriers included tubular, cement, packers, plugs and ball and baffle devices. With isolation along, outside and inside the tubular the primary fracture treatments are completed in sequence from toe to heel to create multiple stages (compartments) along the wellbore. Each consecutive stage is initiated by creating new entry points through the tubular, either by perforations or mechanically activated ports which provide access to the reservoir whilst maintaining isolation up hole. FIGS. 1 & 2 are common completion designs used for multistage fracturing. In the case of an cemented liner with perforation clusters 100, the intermediate casing 101 surrounds the production liner 102. The lateral portion includes a heel 103 and a toe 106. The cement liner 104 contains perforations 105. In the case of an uncemented liner with isolation packers and perforation clusters 200, the intermediate casing 201 surrounds the production liner 202. The lateral portion includes a heel 203 and a toe 207. The liner 204 contains perforations 205 and isolation packers 206. Other completion methods that do not use mechanical barriers to create compartments are open hole completions with or without a liner (tubular). As seen in FIG. 3, an open hole with a perforated liner 300 includes intermediate casing 301 that surrounds the production liner 302. The lateral portion includes a heel 303 and a toe 305. The liner 304 is perforated. As illustrated in FIG. 4, an open hole design 400 includes intermediate casing 401. The lateral portion includes a heel 402 and a toe 403.
Once the primary stimulation treatment is complete, the well is ready to produce fluids. As reservoir fluids are produced from the wellbore the reservoir pressure will decline due to the volumetric drainage within the pore space of the reservoir. Re-fracture treatments (secondary hydraulic fracture treatment) are a common method of enhancing the production of a mature well. A significant difference in primary and secondary fracture treatments is the ability to isolate compartments of the wellbore for stimulation. The entry points created during the primary fracture treatment are a permanent destruction of the wellbore isolation, therefore multistage re-fracturing from toe to heel is not possible without installing new barriers. Installing new barriers is difficult to economically achieve with current technology. Re-fracture treatments often utilize massive fluid volumes at high injections rates in order to create diversion across the large contact area of the reservoir. Self-degrading materials have also been pumped between or during re-fracture treatments to create diversion by bridging off flow into the hydraulic fracture. The successes of these methods has been limited.